widget: expose truncation status of Selectable

This commit adds an exported method to enable widgets to detect
when the text displayed by a Selectable has been truncated. This
can be used to implement proper show-full-text-in-an-overlay
behavior in a parent widget. I haven't attempted to implement
that in core yet, as it is a complex feature involving animation
and pointer interaction.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/text.go

@@ -447,6 +447,12 @@ func (e *textView) MoveCoord(pos image.Point) {
 	e.caret.xoff = 0
 }
 
+// Truncated returns whether the text in the textView is currently
+// truncated due to a restriction on the number of lines.
+func (e *textView) Truncated() bool {
+	return e.index.truncated
+}
+
 func (e *textView) layoutText(lt *text.Shaper) {
 	e.Seek(0, io.SeekStart)
 	var r io.Reader = e